1. Field of the Invention
The present invention relates to an actuator having a displacement detector, more specifically, relates to an actuator in which the displacement detection needs great power consumption, or a number of positions for the displacement detection is limited.
2. Description of the Prior Art
The displacement of position detectors for use in the actuator utilize a change of light, magnetism and electrostatic capacity and a mechanical contact. These various types of detectors can be selected for proper use. In the conventional actuator, the displacement detection is successively carried out for every intermittent drive.
The displacement or position detection consumes almost all amount of assigned power for the act of the detection. For example, as shown in FIG. 9, a photo-detector is comprised of an Si photo-diode 903 as a light source which consumes about 10-20 mW. If the power supply is comprised of a small battery such as a silver battery of button type (capacity 20-100 mWh) and lithium battery of button type (capacity 50-300 mWh), the life of the power supply is shortened due to the successive detection of the displacement.
In a rotary actuator, a detection disc 902 is divided into a given number of angular sections for the successive detection of the angular displacement during the intermittent drives. The detection disc 902 has the given number of slits in case of the photo-detection or the given number of patterns in case of the mechanical contact detection. The provision of slits and patterns needs a space and fabrication cost.